Normally tacky and pressure sensitive adhesive (PSA) materials have been used for well over half a century. Products of this type, which take the form of tapes, labels, and other types of adhesive coated sheets, must be protected from unintended adhesion to other surfaces. Hence, tapes are typically wound into a roll on their own backing and labels are typically laminated to a release sheet to prevent their accidental adhesion to other surfaces and also to prevent their contamination with air-borne dust and other contaminants. In order to allow a roll of tape to be unwound without the undesirable transfer of adhesive to the tape baking, it is customary to provide the tape backing with a low adhesion backsize (LAB). Similarly, the release sheet or liner, to which the adhesive coated label is typically laminated, is supplied with a release coating to permit the easy removal of the liner from the label. This LAB or release coating is expected to reproducibly provide an appropriate level of release to the adhesive of interest, to not deleteriously affect the adhesive, and to be resistant to aging so that the release level remains relatively predictable with time.
The Handbook of Pressure Sensitive Adhesive Technology, 2nd Ed., D. Satas Ed., Van Nostrand Reinhold, N.Y., 1989, Chapter 23, describes polymers which may be used as release agents for PSA tapes. Various polymers of lower critical surface tension such as silicones, fluorine-containing polymers, and long alkyl chain branched polymers are useful as release coatings. Long alkyl chain branched polymers are waxy compounds that can be used to prepare release coatings of medium release value which are especially desirable for PSA tapes. Many release coating patents describe the use of such long alkyl chain branched polymers. For example, Hendricks, U.S. Pat. No. 2,607,711 (1952) describes the use of copolymers of alkyl acrylate and acrylic acid for tape release coatings. According to Hendricks, all acrylates having an alkyl side chain of 16-20 carbon atoms are the more suitable, with octadecyl acrylate being the preferred comonomer.
Examples of other long alkyl chain branched polymers or copolymers include stearyl methacrylate-acrylonitrile copolymer (U.S. Pat. No. 3,502,497); copolymers of stearyl acrylate or methacrylate with other monomers (U.S. Pat. No. 4,241,198); polyvinyl esters such as polyvinyl stearate, polyvinyl palmitate, polyvinyl arachidate, and polyvinyl behenate (U.S. Pat. No. 2,829,073); stearyl maleate-vinyl acetate copolymer (U.S. Pat. No. 3,285,771); polyvinyl stearate, polyvinyl laurate, copolymers of vinyl stearate with vinyl acetate and maleic anhydride, copolymers of octadecyl acrylate with other monomers (U.S. Pat. No. 2,913,355); polyethylene imines acylated with higher fatty acids (U.S. Pat. No. 3,510,342); poly-N-acyl imine (U.S. Pat. No. 3,475,196); solution polymers of vinyl stearate, allyl stearate, or vinyl octadecyl ether with maleic anhydride (U.S. Pat. No. 2,876,894); N-stearyl polyacrylamide (U.S. Pat. No. 3,051,588); solution polymerized stearyl itaconate, monoacetyl itaconate, and monobehenyl itaconate (U.S. Pat. No. 3,052,566); copolymers of N-substituted long straight chain allyl maleamic acids and vinyl monomers (U.S. Pat. No. 3,342,625); and polyvinyl N-octadecyl carbamate prepared by reacting polyvinyl alcohol and octadecyl isocyanate (U.S. Pat. No. 2,532,011).
Other known release coating systems include an organic solvent based polymerization of a vinyl monomer of the general formula CH.sub.2 .dbd.CR'COO(CH.sub.2 CHR"O).sub.n CONHR'" wherein R' and R" each represent a hydrogen or methyl group, R'" represents an alkyl group of at least 12 carbon atoms or a fluoroalkyl group of at least 6 carbon atoms, and n is an integer of 1 to 6. Also known is the polymerization of the vinyl monomer with other vinyl compounds that does not include the preparation of water-borne LABs or release coatings from such monomers. Other known release coating systems include those that use surfactants (emulsifiers) in the stabilization of the polymer. For example, U.S. Pat. No. 5,516,865 (Urquiola) describes a water-borne polymer composition having latex particles formed by emulsion polymerization including an emulsifier at a concentration of about 0.5 to about 8 weight percent based on the total weight of all monomers. The latex particles are formed by emulsion polymerizing long alkyl chain (meth)acrylate monomers and short alkyl chain (meth)acrylate monomers. U.S. Pat. No. 5,225,480 (Tseng et al.) describes a water-borne low adhesion backsize and release coating latex composition prepared by emulsion polymerization including about 0.05 to about 4 weight percent of an emulisifier. The latex particles are stabilized by the emulsifier within the aqueous phase.